// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_TOOLS_BALSA_BALSA_HEADERS_H_
#define NET_TOOLS_BALSA_BALSA_HEADERS_H_

#include <stddef.h>

#include <algorithm>
#include <iosfwd>
#include <iterator>
#include <string>
#include <utility>
#include <vector>

#include "base/logging.h"
#include "base/strings/string_piece.h"
#include "net/tools/balsa/balsa_enums.h"
#include "net/tools/balsa/string_piece_utils.h"

namespace net {

// WARNING:
// Note that -no- char* returned by any function in this
// file is null-terminated.

// This class exists to service the specific needs of BalsaHeaders.
//
// Functional goals:
//   1) provide a backing-store for all of the StringPieces that BalsaHeaders
//      returns. Every StringPiece returned from BalsaHeaders should remain
//      valid until the BalsaHeader's object is cleared, or the header-line is
//      erased.
//   2) provide a backing-store for BalsaFrame, which requires contiguous memory
//      for its fast-path parsing functions. Note that the cost of copying is
//      less than the cost of requiring the parser to do slow-path parsing, as
//      it would have to check for bounds every byte, instead of every 16 bytes.
//
// This class is optimized for the case where headers are stored in one of two
// buffers. It doesn't make a lot of effort to densely pack memory-- in fact,
// it -may- be somewhat memory inefficient. This possible inefficiency allows a
// certain simplicity of implementation and speed which makes it worthwhile.
// If, in the future, better memory density is required, it should be possible
// to reuse the abstraction presented by this object to achieve those goals.
//
// In the most common use-case, this memory inefficiency should be relatively
// small.
//
// Alternate implementations of BalsaBuffer may include:
//  - vector of strings, one per header line (similar to HTTPHeaders)
//  - densely packed strings:
//    - keep a sorted array/map of free-space linked lists or numbers.
//      - use the entry that most closely first your needs.
//    - at this point, perhaps just use a vector of strings, and let
//      the allocator do the right thing.
//
class BalsaBuffer {
public:
    static const size_t kDefaultBlocksize = 4096;
    // We have two friends here. These exist as friends as we
    // want to allow access to the constructors for the test
    // class and the Balsa* classes. We put this into the
    // header file as we want this class to be inlined into the
    // BalsaHeaders implementation, yet be testable.
    friend class BalsaBufferTestSpouse;
    friend class BalsaHeaders;
    friend class BalsaBufferTest;

    // The BufferBlock is a structure used internally by the
    // BalsaBuffer class to store the base buffer pointers to
    // each block, as well as the important metadata for buffer
    // sizes and bytes free.
    struct BufferBlock {
    public:
        char* buffer;
        size_t buffer_size;
        size_t bytes_free;

        size_t bytes_used() const
        {
            return buffer_size - bytes_free;
        }
        char* start_of_unused_bytes() const
        {
            return buffer + bytes_used();
        }

        BufferBlock()
            : buffer(NULL)
            , buffer_size(0)
            , bytes_free(0)
        {
        }
        ~BufferBlock() { }

        BufferBlock(char* buf, size_t size, size_t free)
            : buffer(buf)
            , buffer_size(size)
            , bytes_free(free)
        {
        }
        // Yes we want this to be copyable (it gets stuck into vectors).
        // For this reason, we don't use scoped ptrs, etc. here-- it
        // is more efficient to manage this memory externally to this
        // object.
    };

    typedef std::vector<BufferBlock> Blocks;

    ~BalsaBuffer();

    // Returns the total amount of memory used by the buffer blocks.
    size_t GetTotalBufferBlockSize() const;

    const char* GetPtr(Blocks::size_type block_idx) const
    {
        DCHECK_LT(block_idx, blocks_.size())
            << block_idx << ", " << blocks_.size();
        return blocks_[block_idx].buffer;
    }

    char* GetPtr(Blocks::size_type block_idx)
    {
        DCHECK_LT(block_idx, blocks_.size())
            << block_idx << ", " << blocks_.size();
        return blocks_[block_idx].buffer;
    }

    // This function is different from Write(), as it ensures that the data
    // stored via subsequent calls to this function are all contiguous (and in
    // the order in which these writes happened). This is essentially the same
    // as a string append.
    //
    // You may call this function at any time between object
    // construction/Clear(), and the calling of the
    // NoMoreWriteToContiguousBuffer() function.
    //
    // You must not call this function after the NoMoreWriteToContiguousBuffer()
    // function is called, unless a Clear() has been called since.
    // If you do, the program will abort().
    //
    // This condition is placed upon this code so that calls to Write() can
    // append to the buffer in the first block safely, and without invaliding
    // the StringPiece which it returns.
    //
    // This function's main intended user is the BalsaFrame class, which,
    // for reasons of efficiency, requires that the buffer from which it parses
    // the headers be contiguous.
    //
    void WriteToContiguousBuffer(const base::StringPiece& sp);

    void NoMoreWriteToContiguousBuffer()
    {
        can_write_to_contiguous_buffer_ = false;
    }

    // Takes a StringPiece and writes it to "permanent" storage, then returns a
    // StringPiece which points to that data.  If block_idx != NULL, it will be
    // assigned the index of the block into which the data was stored.
    // Note that the 'permanent' storage in which it stores data may be in
    // the first block IFF the NoMoreWriteToContiguousBuffer function has
    // been called since the last Clear/Construction.
    base::StringPiece Write(const base::StringPiece& sp,
        Blocks::size_type* block_buffer_idx);

    // Reserves "permanent" storage of the size indicated. Returns a pointer to
    // the beginning of that storage, and assigns the index of the block used to
    // block_buffer_idx. This function uses the first block IFF the
    // NoMoreWriteToContiguousBuffer function has been called since the last
    // Clear/Construction.
    char* Reserve(size_t size, Blocks::size_type* block_buffer_idx);

    void Clear();

    void Swap(BalsaBuffer* b);

    void CopyFrom(const BalsaBuffer& b);

    const char* StartOfFirstBlock() const
    {
        return blocks_[0].buffer;
    }

    const char* EndOfFirstBlock() const
    {
        return blocks_[0].buffer + blocks_[0].bytes_used();
    }

    bool can_write_to_contiguous_buffer() const
    {
        return can_write_to_contiguous_buffer_;
    }
    size_t blocksize() const { return blocksize_; }
    Blocks::size_type num_blocks() const { return blocks_.size(); }
    size_t buffer_size(size_t idx) const { return blocks_[idx].buffer_size; }
    size_t bytes_used(size_t idx) const { return blocks_[idx].bytes_used(); }

protected:
    BalsaBuffer();

    explicit BalsaBuffer(size_t blocksize);

    BufferBlock AllocBlock();

    BufferBlock AllocCustomBlock(size_t blocksize);

    BufferBlock CopyBlock(const BufferBlock& b);

    // Cleans up the object.
    // The block at start_idx, and all subsequent blocks
    // will be cleared and have associated memory deleted.
    void CleanupBlocksStartingFrom(Blocks::size_type start_idx);

    // A container of BufferBlocks
    Blocks blocks_;

    // The default allocation size for a block.
    // In general, blocksize_ bytes will be allocated for
    // each buffer.
    size_t blocksize_;

    // If set to true, then the first block cannot be used for Write() calls as
    // the WriteToContiguous... function will modify the base pointer for this
    // block, and the Write() calls need to be sure that the base pointer will
    // not be changing in order to provide the user with StringPieces which
    // continue to be valid.
    bool can_write_to_contiguous_buffer_;
};

////////////////////////////////////////////////////////////////////////////////

// All of the functions in the BalsaHeaders class use string pieces, by either
// using the StringPiece class, or giving an explicit size and char* (as these
// are the native representation for these string pieces).
// This is done for several reasons.
//  1) This minimizes copying/allocation/deallocation as compared to using
//  string parameters
//  2) This reduces the number of strlen() calls done (as the length of any
//  string passed in is relatively likely to be known at compile time, and for
//  those strings passed back we obviate the need for a strlen() to determine
//  the size of new storage allocations if a new allocation is required.
//  3) This class attempts to store all of its data in two linear buffers in
//  order to enhance the speed of parsing and writing out to a buffer. As a
//  result, many string pieces are -not- terminated by '\0', and are not
//  c-strings.  Since this is the case, we must delineate the length of the
//  string explicitly via a length.
//
//  WARNING:  The side effect of using StringPiece is that if the underlying
//  buffer changes (due to modifying the headers) the StringPieces which point
//  to the data which was modified, may now contain "garbage", and should not
//  be dereferenced.
//  For example, If you fetch some component of the first-line, (request or
//  response), and then you modify the first line, the StringPieces you
//  originally received from the original first-line may no longer be valid).
//
//  StringPieces pointing to pieces of header lines which have not been
//  erased() or modified should be valid until the object is cleared or
//  destroyed.

class BalsaHeaders {
public:
    struct HeaderLineDescription {
        HeaderLineDescription(size_t first_character_index,
            size_t key_end_index,
            size_t value_begin_index,
            size_t last_character_index,
            size_t buffer_base_index)
            : first_char_idx(first_character_index)
            , key_end_idx(key_end_index)
            , value_begin_idx(value_begin_index)
            , last_char_idx(last_character_index)
            , buffer_base_idx(buffer_base_index)
            , skip(false)
        {
        }

        HeaderLineDescription()
            : first_char_idx(0)
            , key_end_idx(0)
            , value_begin_idx(0)
            , last_char_idx(0)
            , buffer_base_idx(0)
            , skip(false)
        {
        }

        size_t first_char_idx;
        size_t key_end_idx;
        size_t value_begin_idx;
        size_t last_char_idx;
        BalsaBuffer::Blocks::size_type buffer_base_idx;
        bool skip;
    };

    typedef std::vector<base::StringPiece> HeaderTokenList;
    friend bool ParseHTTPFirstLine(const char* begin,
        const char* end,
        bool is_request,
        size_t max_request_uri_length,
        BalsaHeaders* headers,
        BalsaFrameEnums::ErrorCode* error_code);

protected:
    typedef std::vector<HeaderLineDescription> HeaderLines;

    // Why these base classes (iterator_base, reverse_iterator_base)?  Well, if
    // we do want to export both iterator and const_iterator types (currently we
    // only have const_iterator), then this is useful to avoid code duplication.
    // Additionally, having this base class makes comparisons of iterators of
    // different types (they're different types to ensure that operator= and
    // constructors do not work in the places where they're expected to not work)
    // work properly. There could be as many as 4 iterator types, all based on
    // the same data as iterator_base... so it makes sense to simply have some
    // base classes.

    class iterator_base {
    public:
        friend class BalsaHeaders;
        friend class reverse_iterator_base;
        typedef std::pair<base::StringPiece, base::StringPiece> StringPiecePair;
        typedef StringPiecePair value_type;
        typedef value_type& reference;
        typedef value_type* pointer;

        typedef std::forward_iterator_tag iterator_category;
        typedef ptrdiff_t difference_type;

        typedef iterator_base self;

        // default constructor.
        iterator_base();

        // copy constructor.
        iterator_base(const iterator_base& it);

        reference operator*() const
        {
            return Lookup(idx_);
        }

        pointer operator->() const
        {
            return &(this->operator*());
        }

        bool operator==(const self& it) const
        {
            return idx_ == it.idx_;
        }

        bool operator<(const self& it) const
        {
            return idx_ < it.idx_;
        }

        bool operator<=(const self& it) const
        {
            return idx_ <= it.idx_;
        }

        bool operator!=(const self& it) const
        {
            return !(*this == it);
        }

        bool operator>(const self& it) const
        {
            return it < *this;
        }

        bool operator>=(const self& it) const
        {
            return it <= *this;
        }

        // This mainly exists so that we can have interesting output for
        // unittesting. The EXPECT_EQ, EXPECT_NE functions require that
        // operator<< work for the classes it sees.  It would be better if there
        // was an additional traits-like system for the gUnit output... but oh
        // well.
        std::ostream& operator<<(std::ostream& os) const;

    protected:
        iterator_base(const BalsaHeaders* headers, HeaderLines::size_type index);

        void increment()
        {
            const HeaderLines& header_lines = headers_->header_lines_;
            const HeaderLines::size_type header_lines_size = header_lines.size();
            const HeaderLines::size_type original_idx = idx_;
            do {
                ++idx_;
            } while (idx_ < header_lines_size && header_lines[idx_].skip == true);
            // The condition below exists so that ++(end() - 1) == end(), even
            // if there are only 'skip == true' elements between the end() iterator
            // and the end of the vector of HeaderLineDescriptions.
            // TODO(fenix): refactor this list so that we don't have to do
            // linear scanning through skipped headers (and this condition is
            // then unnecessary)
            if (idx_ == header_lines_size) {
                idx_ = original_idx + 1;
            }
        }

        void decrement()
        {
            const HeaderLines& header_lines = headers_->header_lines_;
            const HeaderLines::size_type header_lines_size = header_lines.size();
            const HeaderLines::size_type original_idx = idx_;
            do {
                --idx_;
            } while (idx_ < header_lines_size && header_lines[idx_].skip == true);
            // The condition below exists so that --(rbegin() + 1) == rbegin(), even
            // if there are only 'skip == true' elements between the rbegin() iterator
            // and the beginning of the vector of HeaderLineDescriptions.
            // TODO(fenix): refactor this list so that we don't have to do
            // linear scanning through skipped headers (and this condition is
            // then unnecessary)
            if (idx_ > header_lines_size) {
                idx_ = original_idx - 1;
            }
        }

        reference Lookup(HeaderLines::size_type index) const
        {
            DCHECK_LT(index, headers_->header_lines_.size());
            const HeaderLineDescription& line = headers_->header_lines_[index];
            const char* stream_begin = headers_->GetPtr(line.buffer_base_idx);
            value_ = value_type(
                base::StringPiece(stream_begin + line.first_char_idx,
                    line.key_end_idx - line.first_char_idx),
                base::StringPiece(stream_begin + line.value_begin_idx,
                    line.last_char_idx - line.value_begin_idx));
            DCHECK_GE(line.key_end_idx, line.first_char_idx);
            DCHECK_GE(line.last_char_idx, line.value_begin_idx);
            return value_;
        }

        const BalsaHeaders* headers_;
        HeaderLines::size_type idx_;
        mutable StringPiecePair value_;
    };

    class reverse_iterator_base : public iterator_base {
    public:
        typedef reverse_iterator_base self;
        typedef iterator_base::reference reference;
        typedef iterator_base::pointer pointer;
        using iterator_base::headers_;
        using iterator_base::idx_;

        reverse_iterator_base()
            : iterator_base()
        {
        }

        // This constructor is no explicit purposely.
        reverse_iterator_base(const iterator_base& it)
            : // NOLINT
            iterator_base(it)
        {
        }

        self& operator=(const iterator_base& it)
        {
            idx_ = it.idx_;
            headers_ = it.headers_;
            return *this;
        }

        self& operator=(const reverse_iterator_base& it)
        {
            idx_ = it.idx_;
            headers_ = it.headers_;
            return *this;
        }

        reference operator*() const
        {
            return Lookup(idx_ - 1);
        }

        pointer operator->() const
        {
            return &(this->operator*());
        }

        reverse_iterator_base(const reverse_iterator_base& it)
            : iterator_base(it)
        {
        }

    protected:
        void increment()
        {
            --idx_;
            iterator_base::decrement();
            ++idx_;
        }

        void decrement()
        {
            ++idx_;
            iterator_base::increment();
            --idx_;
        }

        reverse_iterator_base(const BalsaHeaders* headers,
            HeaderLines::size_type index)
            : iterator_base(headers, index)
        {
        }
    };

public:
    class const_header_lines_iterator : public iterator_base {
        friend class BalsaHeaders;

    public:
        typedef const_header_lines_iterator self;
        const_header_lines_iterator()
            : iterator_base()
        {
        }

        const_header_lines_iterator(const const_header_lines_iterator& it)
            : iterator_base(it.headers_, it.idx_)
        {
        }

        self& operator++()
        {
            iterator_base::increment();
            return *this;
        }

        self& operator--()
        {
            iterator_base::decrement();
            return *this;
        }

    protected:
        const_header_lines_iterator(const BalsaHeaders* headers,
            HeaderLines::size_type index)
            : iterator_base(headers, index)
        {
        }
    };

    class const_reverse_header_lines_iterator : public reverse_iterator_base {
    public:
        typedef const_reverse_header_lines_iterator self;
        const_reverse_header_lines_iterator()
            : reverse_iterator_base()
        {
        }

        const_reverse_header_lines_iterator(
            const const_header_lines_iterator& it)
            : reverse_iterator_base(it.headers_, it.idx_)
        {
        }

        const_reverse_header_lines_iterator(
            const const_reverse_header_lines_iterator& it)
            : reverse_iterator_base(it.headers_, it.idx_)
        {
        }

        const_header_lines_iterator base()
        {
            return const_header_lines_iterator(headers_, idx_);
        }

        self& operator++()
        {
            reverse_iterator_base::increment();
            return *this;
        }

        self& operator--()
        {
            reverse_iterator_base::decrement();
            return *this;
        }

    protected:
        const_reverse_header_lines_iterator(const BalsaHeaders* headers,
            HeaderLines::size_type index)
            : reverse_iterator_base(headers, index)
        {
        }

        friend class BalsaHeaders;
    };

    // An iterator that only stops at lines with a particular key.
    // See also GetIteratorForKey.
    //
    // Check against header_lines_key_end() to determine when iteration is
    // finished. header_lines_end() will also work.
    class const_header_lines_key_iterator : public iterator_base {
        friend class BalsaHeaders;

    public:
        typedef const_header_lines_key_iterator self;
        const_header_lines_key_iterator(const const_header_lines_key_iterator&);

        self& operator++()
        {
            do {
                iterator_base::increment();
            } while (!AtEnd() && !base::EqualsCaseInsensitiveASCII(key_, (**this).first));
            return *this;
        }

        void operator++(int ignore)
        {
            ++(*this);
        }

        // Only forward-iteration makes sense, so no operator-- defined.

    private:
        const_header_lines_key_iterator(const BalsaHeaders* headers,
            HeaderLines::size_type index,
            const base::StringPiece& key);

        // Should only be used for creating an end iterator.
        const_header_lines_key_iterator(const BalsaHeaders* headers,
            HeaderLines::size_type index);

        bool AtEnd() const
        {
            return *this >= headers_->header_lines_end();
        }

        base::StringPiece key_;
    };

    // TODO(fenix): Revisit the amount of bytes initially allocated to the second
    // block of the balsa_buffer_. It may make sense to pre-allocate some amount
    // (roughly the amount we'd append in new headers such as X-User-Ip, etc.)
    BalsaHeaders();
    ~BalsaHeaders();

    const_header_lines_iterator header_lines_begin()
    {
        return HeaderLinesBeginHelper<const_header_lines_iterator>();
    }

    const_header_lines_iterator header_lines_begin() const
    {
        return HeaderLinesBeginHelper<const_header_lines_iterator>();
    }

    const_header_lines_iterator header_lines_end()
    {
        return HeaderLinesEndHelper<const_header_lines_iterator>();
    }

    const_header_lines_iterator header_lines_end() const
    {
        return HeaderLinesEndHelper<const_header_lines_iterator>();
    }

    const_reverse_header_lines_iterator header_lines_rbegin()
    {
        return const_reverse_header_lines_iterator(header_lines_end());
    }

    const_reverse_header_lines_iterator header_lines_rbegin() const
    {
        return const_reverse_header_lines_iterator(header_lines_end());
    }

    const_reverse_header_lines_iterator header_lines_rend()
    {
        return const_reverse_header_lines_iterator(header_lines_begin());
    }

    const_reverse_header_lines_iterator header_lines_rend() const
    {
        return const_reverse_header_lines_iterator(header_lines_begin());
    }

    const_header_lines_key_iterator header_lines_key_end() const
    {
        return HeaderLinesEndHelper<const_header_lines_key_iterator>();
    }

    void erase(const const_header_lines_iterator& it)
    {
        DCHECK_EQ(it.headers_, this);
        DCHECK_LT(it.idx_, header_lines_.size());
        DCHECK_GE(it.idx_, 0u);
        header_lines_[it.idx_].skip = true;
    }

    void Clear();

    void Swap(BalsaHeaders* other);

    void CopyFrom(const BalsaHeaders& other);

    void HackHeader(const base::StringPiece& key, const base::StringPiece& value);

    // Same as AppendToHeader, except that it will attempt to preserve
    // header ordering.
    // Note that this will always append to an existing header, if available,
    // without moving the header around, or collapsing multiple header lines
    // with the same key together. For this reason, it only 'attempts' to
    // preserve header ordering.
    // TODO(fenix): remove this function and rename all occurances
    // of it in the code to AppendToHeader when the condition above
    // has been satisified.
    void HackAppendToHeader(const base::StringPiece& key,
        const base::StringPiece& value);

    // Replaces header entries with key 'key' if they exist, or appends
    // a new header if none exist.  See 'AppendHeader' below for additional
    // comments about ContentLength and TransferEncoding headers. Note that this
    // will allocate new storage every time that it is called.
    // TODO(fenix): modify this function to reuse existing storage
    // if it is available.
    void ReplaceOrAppendHeader(const base::StringPiece& key,
        const base::StringPiece& value);

    // Append a new header entry to the header object. Clients who wish to append
    // Content-Length header should use SetContentLength() method instead of
    // adding the content length header using AppendHeader (manually adding the
    // content length header will not update the content_length_ and
    // content_length_status_ values).
    // Similarly, clients who wish to add or remove the transfer encoding header
    // in order to apply or remove chunked encoding should use SetChunkEncoding()
    // instead.
    void AppendHeader(const base::StringPiece& key,
        const base::StringPiece& value);

    // Appends ',value' to an existing header named 'key'.  If no header with the
    // correct key exists, it will call AppendHeader(key, value).  Calling this
    // function on a key which exists several times in the headers will produce
    // unpredictable results.
    void AppendToHeader(const base::StringPiece& key,
        const base::StringPiece& value);

    // Prepends 'value,' to an existing header named 'key'.  If no header with the
    // correct key exists, it will call AppendHeader(key, value).  Calling this
    // function on a key which exists several times in the headers will produce
    // unpredictable results.
    void PrependToHeader(const base::StringPiece& key,
        const base::StringPiece& value);

    const base::StringPiece GetHeader(const base::StringPiece& key) const;

    // Iterates over all currently valid header lines, appending their
    // values into the vector 'out', in top-to-bottom order.
    // Header-lines which have been erased are not currently valid, and
    // will not have their values appended. Empty values will be
    // represented as empty string. If 'key' doesn't exist in the headers at
    // all, out will not be changed. We do not clear the vector out
    // before adding new entries. If there are header lines with matching
    // key but empty value then they are also added to the vector out.
    // (Basically empty values are not treated in any special manner).
    //
    // Example:
    // Input header:
    // "GET / HTTP/1.0\r\n"
    //    "key1: v1\r\n"
    //    "key1: \r\n"
    //    "key1:\r\n"
    //    "key1:  v1\r\n"
    //    "key1:v2\r\n"
    //
    //  vector out is initially: ["foo"]
    //  vector out after GetAllOfHeader("key1", &out) is:
    // ["foo", "v1", "", "", "v2", "v1", "v2"]

    void GetAllOfHeader(const base::StringPiece& key,
        std::vector<base::StringPiece>* out) const;

    // Joins all values for key into a comma-separated string in out.
    // More efficient than calling JoinStrings on result of GetAllOfHeader if
    // you don't need the intermediate vector<StringPiece>.
    void GetAllOfHeaderAsString(const base::StringPiece& key,
        std::string* out) const;

    // Returns true if RFC 2616 Section 14 indicates that header can
    // have multiple values.
    static bool IsMultivaluedHeader(const base::StringPiece& header);

    // Determine if a given header is present.
    inline bool HasHeader(const base::StringPiece& key) const
    {
        return (GetConstHeaderLinesIterator(key, header_lines_.begin()) != header_lines_.end());
    }

    // Returns true iff any header 'key' exists with non-empty value.
    bool HasNonEmptyHeader(const base::StringPiece& key) const;

    const_header_lines_iterator GetHeaderPosition(
        const base::StringPiece& key) const;

    // Returns a forward-only iterator that only stops at lines matching key.
    // String backing 'key' must remain valid for lifetime of iterator.
    //
    // Check returned iterator against header_lines_key_end() to determine when
    // iteration is finished.
    const_header_lines_key_iterator GetIteratorForKey(
        const base::StringPiece& key) const;

    void RemoveAllOfHeader(const base::StringPiece& key);

    // Removes all headers starting with 'key' [case insensitive]
    void RemoveAllHeadersWithPrefix(const base::StringPiece& key);

    // Returns the lower bound of memory  used by this header object, including
    // all internal buffers and data structure. Some of the memory used cannot be
    // directly measure. For example, memory used for bookkeeping by standard
    // containers.
    size_t GetMemoryUsedLowerBound() const;

    // Returns the upper bound on the required buffer space to fully write out
    // the header object (this include the first line, all header lines, and the
    // final CRLF that marks the ending of the header).
    size_t GetSizeForWriteBuffer() const;

    // The following WriteHeader* methods are template member functions that
    // place one requirement on the Buffer class: it must implement a Write
    // method that takes a pointer and a length. The buffer passed in is not
    // required to be stretchable. For non-stretchable buffers, the user must
    // call GetSizeForWriteBuffer() to find out the upper bound on the output
    // buffer space required to make sure that the entire header is serialized.
    // BalsaHeaders will not check that there is adequate space in the buffer
    // object during the write.

    // Writes the entire header and the final CRLF that marks the end of the HTTP
    // header section to the buffer. After this method returns, no more header
    // data should be written to the buffer.
    template <typename Buffer>
    void WriteHeaderAndEndingToBuffer(Buffer* buffer) const
    {
        WriteToBuffer(buffer);
        WriteHeaderEndingToBuffer(buffer);
    }

    // Writes the final CRLF to the buffer to terminate the HTTP header section.
    // After this method returns, no more header data should be written to the
    // buffer.
    template <typename Buffer>
    static void WriteHeaderEndingToBuffer(Buffer* buffer)
    {
        buffer->Write("\r\n", 2);
    }

    // Writes the entire header to the buffer without the CRLF that terminates
    // the HTTP header. This lets users append additional header lines using
    // WriteHeaderLineToBuffer and then terminate the header with
    // WriteHeaderEndingToBuffer as the header is serialized to the
    // buffer, without having to first copy the header.
    template <typename Buffer>
    void WriteToBuffer(Buffer* buffer) const
    {
        // write the first line.
        const size_t firstline_len = whitespace_4_idx_ - non_whitespace_1_idx_;
        const char* stream_begin = GetPtr(firstline_buffer_base_idx_);
        buffer->Write(stream_begin + non_whitespace_1_idx_, firstline_len);
        buffer->Write("\r\n", 2);
        const HeaderLines::size_type end = header_lines_.size();
        for (HeaderLines::size_type i = 0; i < end; ++i) {
            const HeaderLineDescription& line = header_lines_[i];
            if (line.skip) {
                continue;
            }
            const char* line_ptr = GetPtr(line.buffer_base_idx);
            WriteHeaderLineToBuffer(
                buffer,
                base::StringPiece(line_ptr + line.first_char_idx,
                    line.key_end_idx - line.first_char_idx),
                base::StringPiece(line_ptr + line.value_begin_idx,
                    line.last_char_idx - line.value_begin_idx));
        }
    }

    // Takes a header line in the form of a key/value pair and append it to the
    // buffer. This function should be called after WriteToBuffer to
    // append additional header lines to the header without copying the header.
    // When the user is done with appending to the buffer,
    // WriteHeaderEndingToBuffer must be used to terminate the HTTP
    // header in the buffer. This method is a no-op if key is empty.
    template <typename Buffer>
    static void WriteHeaderLineToBuffer(Buffer* buffer,
        const base::StringPiece& key,
        const base::StringPiece& value)
    {
        // if the key is empty, we don't want to write the rest because it
        // will not be a well-formed header line.
        if (!key.empty()) {
            buffer->Write(key.data(), key.size());
            buffer->Write(": ", 2);
            buffer->Write(value.data(), value.size());
            buffer->Write("\r\n", 2);
        }
    }

    // Dump the textural representation of the header object to a string, which
    // is suitable for writing out to logs. All CRLF will be printed out as \n.
    // This function can be called on a header object in any state. The header
    // content is appended to the string; the original content is not cleared.
    void DumpHeadersToString(std::string* str) const;

    // Calls DumpHeadersToString to dump the textural representation of the header
    // object to a string. Raw header data will be printed out if the header
    // object is not completely parsed, e.g., when there was an error in the
    // middle of parsing.
    void DumpToString(std::string* str) const;

    const base::StringPiece first_line() const
    {
        DCHECK_GE(whitespace_4_idx_, non_whitespace_1_idx_);
        return base::StringPiece(BeginningOfFirstLine() + non_whitespace_1_idx_,
            whitespace_4_idx_ - non_whitespace_1_idx_);
    }

    // Returns the parsed value of the response code if it has been parsed.
    // Guaranteed to return 0 when unparsed (though it is a much better idea to
    // verify that the BalsaFrame had no errors while parsing).
    // This may return response codes which are outside the normal bounds of
    // HTTP response codes-- it is up to the user of this class to ensure that
    // the response code is one which is interpretable.
    size_t parsed_response_code() const { return parsed_response_code_; }

    const base::StringPiece request_method() const
    {
        DCHECK_GE(whitespace_2_idx_, non_whitespace_1_idx_);
        return base::StringPiece(BeginningOfFirstLine() + non_whitespace_1_idx_,
            whitespace_2_idx_ - non_whitespace_1_idx_);
    }

    const base::StringPiece response_version() const
    {
        // Note: There is no difference between request_method() and
        // response_version(). They both could be called
        // GetFirstTokenFromFirstline()... but that wouldn't be anywhere near as
        // descriptive.
        return request_method();
    }

    const base::StringPiece request_uri() const
    {
        DCHECK_GE(whitespace_3_idx_, non_whitespace_2_idx_);
        return base::StringPiece(BeginningOfFirstLine() + non_whitespace_2_idx_,
            whitespace_3_idx_ - non_whitespace_2_idx_);
    }

    const base::StringPiece response_code() const
    {
        // Note: There is no difference between request_uri() and response_code().
        // They both could be called GetSecondtTokenFromFirstline(), but, as noted
        // in an earlier comment, that wouldn't be as descriptive.
        return request_uri();
    }

    const base::StringPiece request_version() const
    {
        DCHECK_GE(whitespace_4_idx_, non_whitespace_3_idx_);
        return base::StringPiece(BeginningOfFirstLine() + non_whitespace_3_idx_,
            whitespace_4_idx_ - non_whitespace_3_idx_);
    }

    const base::StringPiece response_reason_phrase() const
    {
        // Note: There is no difference between request_version() and
        // response_reason_phrase(). They both could be called
        // GetThirdTokenFromFirstline(), but, as noted in an earlier comment, that
        // wouldn't be as descriptive.
        return request_version();
    }

    // Note that SetFirstLine will not update the internal indices for the
    // various bits of the first-line (and may set them all to zero).
    // If you'd like to use the accessors for the various bits of the firstline,
    // then you should use the Set* functions, or SetFirstlineFromStringPieces,
    // below, instead.
    //
    void SetFirstlineFromStringPieces(const base::StringPiece& firstline_a,
        const base::StringPiece& firstline_b,
        const base::StringPiece& firstline_c);

    void SetRequestFirstlineFromStringPieces(const base::StringPiece& method,
        const base::StringPiece& uri,
        const base::StringPiece& version)
    {
        SetFirstlineFromStringPieces(method, uri, version);
    }

    void SetResponseFirstlineFromStringPieces(
        const base::StringPiece& version,
        const base::StringPiece& code,
        const base::StringPiece& reason_phrase)
    {
        SetFirstlineFromStringPieces(version, code, reason_phrase);
    }

    // These functions are exactly the same, except that their names are
    // different. This is done so that the code using this class is more
    // expressive.
    void SetRequestMethod(const base::StringPiece& method);
    void SetResponseVersion(const base::StringPiece& version);

    void SetRequestUri(const base::StringPiece& uri);
    void SetResponseCode(const base::StringPiece& code);
    void set_parsed_response_code(size_t parsed_response_code)
    {
        parsed_response_code_ = parsed_response_code;
    }
    void SetParsedResponseCodeAndUpdateFirstline(size_t parsed_response_code);

    // These functions are exactly the same, except that their names are
    // different. This is done so that the code using this class is more
    // expressive.
    void SetRequestVersion(const base::StringPiece& version);
    void SetResponseReasonPhrase(const base::StringPiece& reason_phrase);

    // The biggest problem with SetFirstLine is that we don't want to use a
    // separate buffer for it.  The second biggest problem with it is that the
    // first biggest problem requires that we store offsets into a buffer instead
    // of pointers into a buffer. Cuteness aside, SetFirstLine doesn't parse
    // the individual fields of the firstline, and so accessors to those fields
    // will not work properly after calling SetFirstLine. If you want those
    // accessors to work, use the Set* functions above this one.
    // SetFirstLine is stuff useful, however, if all you care about is correct
    // serialization with the rest of the header object.
    void SetFirstLine(const base::StringPiece& line);

    // Simple accessors to some of the internal state
    bool transfer_encoding_is_chunked() const
    {
        return transfer_encoding_is_chunked_;
    }

    static bool ResponseCodeImpliesNoBody(size_t code)
    {
        // From HTTP spec section 6.1.1 all 1xx responses must not have a body,
        // as well as 204 No Content and 304 Not Modified.
        return ((code >= 100) && (code <= 199)) || (code == 204) || (code == 304);
    }

    // Note: never check this for requests. Nothing bad will happen if you do,
    // but spec does not allow requests framed by connection close.
    // TODO(vitaliyl): refactor.
    bool is_framed_by_connection_close() const
    {
        // We declare that response is framed by connection close if it has no
        // content-length, no transfer encoding, and is allowed to have a body by
        // the HTTP spec.
        // parsed_response_code_ is 0 for requests, so ResponseCodeImpliesNoBody
        // will return false.
        return (content_length_status_ == BalsaHeadersEnums::NO_CONTENT_LENGTH) && !transfer_encoding_is_chunked_ && !ResponseCodeImpliesNoBody(parsed_response_code_);
    }

    size_t content_length() const { return content_length_; }
    BalsaHeadersEnums::ContentLengthStatus content_length_status() const
    {
        return content_length_status_;
    }

    // SetContentLength and SetChunkEncoding modifies the header object to use
    // content-length and transfer-encoding headers in a consistent manner. They
    // set all internal flags and status so client can get a consistent view from
    // various accessors.
    void SetContentLength(size_t length);
    void SetChunkEncoding(bool chunk_encode);

protected:
    friend class BalsaFrame;
    friend class SpdyFrame;
    friend class HTTPMessage;
    friend class BalsaHeadersTokenUtils;

    const char* BeginningOfFirstLine() const
    {
        return GetPtr(firstline_buffer_base_idx_);
    }

    char* GetPtr(BalsaBuffer::Blocks::size_type block_idx)
    {
        return balsa_buffer_.GetPtr(block_idx);
    }

    const char* GetPtr(BalsaBuffer::Blocks::size_type block_idx) const
    {
        return balsa_buffer_.GetPtr(block_idx);
    }

    void WriteFromFramer(const char* ptr, size_t size)
    {
        balsa_buffer_.WriteToContiguousBuffer(base::StringPiece(ptr, size));
    }

    void DoneWritingFromFramer()
    {
        balsa_buffer_.NoMoreWriteToContiguousBuffer();
    }

    const char* OriginalHeaderStreamBegin() const
    {
        return balsa_buffer_.StartOfFirstBlock();
    }

    const char* OriginalHeaderStreamEnd() const
    {
        return balsa_buffer_.EndOfFirstBlock();
    }

    size_t GetReadableBytesFromHeaderStream() const
    {
        return OriginalHeaderStreamEnd() - OriginalHeaderStreamBegin();
    }

    void GetReadablePtrFromHeaderStream(const char** p, size_t* s)
    {
        *p = OriginalHeaderStreamBegin();
        *s = GetReadableBytesFromHeaderStream();
    }

    base::StringPiece GetValueFromHeaderLineDescription(
        const HeaderLineDescription& line) const;

    void AddAndMakeDescription(const base::StringPiece& key,
        const base::StringPiece& value,
        HeaderLineDescription* d);

    void AppendOrPrependAndMakeDescription(const base::StringPiece& key,
        const base::StringPiece& value,
        bool append,
        HeaderLineDescription* d);

    // Removes all header lines with the given key starting at start.
    void RemoveAllOfHeaderStartingAt(const base::StringPiece& key,
        HeaderLines::iterator start);

    // If the 'key' does not exist in the headers, calls
    // AppendHeader(key, value).  Otherwise if append is true, appends ',value'
    // to the first existing header with key 'key'.  If append is false, prepends
    // 'value,' to the first existing header with key 'key'.
    void AppendOrPrependToHeader(const base::StringPiece& key,
        const base::StringPiece& value,
        bool append);

    HeaderLines::const_iterator GetConstHeaderLinesIterator(
        const base::StringPiece& key,
        HeaderLines::const_iterator start) const;

    HeaderLines::iterator GetHeaderLinesIteratorNoSkip(
        const base::StringPiece& key,
        HeaderLines::iterator start);

    HeaderLines::iterator GetHeaderLinesIterator(
        const base::StringPiece& key,
        HeaderLines::iterator start);

    template <typename IteratorType>
    const IteratorType HeaderLinesBeginHelper() const
    {
        if (header_lines_.empty()) {
            return IteratorType(this, 0);
        }
        const HeaderLines::size_type header_lines_size = header_lines_.size();
        for (HeaderLines::size_type i = 0; i < header_lines_size; ++i) {
            if (header_lines_[i].skip == false) {
                return IteratorType(this, i);
            }
        }
        return IteratorType(this, 0);
    }

    template <typename IteratorType>
    const IteratorType HeaderLinesEndHelper() const
    {
        if (header_lines_.empty()) {
            return IteratorType(this, 0);
        }
        const HeaderLines::size_type header_lines_size = header_lines_.size();
        HeaderLines::size_type i = header_lines_size;
        do {
            --i;
            if (header_lines_[i].skip == false) {
                return IteratorType(this, i + 1);
            }
        } while (i != 0);
        return IteratorType(this, 0);
    }

    // At the moment, this function will always return the original headers.
    // In the future, it may not do so after erasing header lines, modifying
    // header lines, or modifying the first line.
    // For this reason, it is strongly suggested that use of this function is
    // only acceptable for the purpose of debugging parse errors seen by the
    // BalsaFrame class.
    base::StringPiece OriginalHeadersForDebugging() const
    {
        return base::StringPiece(OriginalHeaderStreamBegin(),
            OriginalHeaderStreamEnd() - OriginalHeaderStreamBegin());
    }

    BalsaBuffer balsa_buffer_;

    size_t content_length_;
    BalsaHeadersEnums::ContentLengthStatus content_length_status_;
    size_t parsed_response_code_;
    // HTTP firstlines all have the following structure:
    //  LWS         NONWS  LWS    NONWS   LWS    NONWS   NOTCRLF  CRLF
    //  [\t \r\n]+ [^\t ]+ [\t ]+ [^\t ]+ [\t ]+ [^\t ]+ [^\r\n]+ "\r\n"
    //  ws1        nws1    ws2    nws2    ws3    nws3             ws4
    //  |          [-------)      [-------)      [----------------)
    //    REQ:     method         request_uri    version
    //   RESP:     version        statuscode     reason
    //
    //   The first NONWS->LWS component we'll call firstline_a.
    //   The second firstline_b, and the third firstline_c.
    //
    //   firstline_a goes from nws1 to (but not including) ws2
    //   firstline_b goes from nws2 to (but not including) ws3
    //   firstline_c goes from nws3 to (but not including) ws4
    //
    // In the code:
    //    ws1 == whitespace_1_idx_
    //   nws1 == non_whitespace_1_idx_
    //    ws2 == whitespace_2_idx_
    //   nws2 == non_whitespace_2_idx_
    //    ws3 == whitespace_3_idx_
    //   nws3 == non_whitespace_3_idx_
    //    ws4 == whitespace_4_idx_
    BalsaBuffer::Blocks::size_type firstline_buffer_base_idx_;
    size_t whitespace_1_idx_;
    size_t non_whitespace_1_idx_;
    size_t whitespace_2_idx_;
    size_t non_whitespace_2_idx_;
    size_t whitespace_3_idx_;
    size_t non_whitespace_3_idx_;
    size_t whitespace_4_idx_;
    size_t end_of_firstline_idx_;

    bool transfer_encoding_is_chunked_;

    HeaderLines header_lines_;
};

} // namespace net

#endif // NET_TOOLS_BALSA_BALSA_HEADERS_H_
